[IndVars] Don't break dominance in `eliminateIdentitySCEV`

Summary:
After r249211, `getSCEV(X) == getSCEV(Y)` does not guarantee that X and
Y are related in the dominator tree, even if X is an operand to Y (I've
included a toy example in comments, and a real example as a test case).

This commit changes `SimplifyIndVar` to require a `DominatorTree`.  I
don't think this is a problem because `ScalarEvolution` requires it
anyway.

Fixes PR25051.

Depends on D13459.

Reviewers: atrick, hfinkel

Subscribers: joker.eph, llvm-commits, sanjoy

Differential Revision: http://reviews.llvm.org/D13460

llvm-svn: 249471

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index 95d31d86644..b7e248860c5 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -499,7 +499,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
     // Simplify any new induction variables in the partially unrolled loop.
     if (SE && !CompletelyUnroll) {
       SmallVector<WeakVH, 16> DeadInsts;
-      simplifyLoopIVs(L, SE, LPM, DeadInsts);
+      simplifyLoopIVs(L, SE, DT, LPM, DeadInsts);
 
       // Aggressively clean up dead instructions that simplifyLoopIVs already
       // identified. Any remaining should be cleaned up below.